Research is being conducted on multi-radio access technology (RAT) using convergence of heterogeneous communication networks. For example, a multi-RAT user equipment (UE) supports both a cellular network and a wireless local area network (WLAN). This multi-RAT UE can be selectively connected to only one of a plurality of RATs, but cannot be simultaneously connected to them. That is, even when a UE currently has multi-RAT capability, the UE cannot transmit/receive data simultaneously using different RATs.
In addition, according to a conventional multi-RAT technology, different RATs operate independently from each other and thus a whole system cannot operate integrally or systematically. For example, when a UE connected to a cellular network attempts to be switched to a WLAN, the UE should autonomously perform a series of operations related to scanning for and connection to the WLAN with no help of the cellular network and no preliminary information about the WLAN.